1. Field of the Invention
The present invention relates generally to tuning of optical fiber structures. More particularly, the present invention relates to tuning, protection, and environmental isolation of distributed feedback fiber lasers.
2.Related Art
Lasers have found use in a variety of applications, including displays, optical printing, optical recording, and communications. Distributed feedback (DFB) fiber lasers, in particular, have proven useful in those applications where the single-mode operation, narrow optical linewidth, and low noise performance of DFB fiber lasers are particularly advantageous. Tuning of DFB fiber laser optical frequency is generally required to correct initial manufacturing tolerances, and various fixed schemes to accomplish initial tuning are known. In many applications, very stable laser optical frequency is required, however, and maintaining long-term stability has proved challenging.
Controlled changes in temperature or controlled application of mechanical strain to the fiber may be used to tune the optical frequency of a DFB fiber laser. Changes in temperature and mechanical strain result in changes to the period of gratings impressed into the fiber resulting in a change in the optical frequency of the DFB fiber laser. Thermal tuning by adjusting the temperature of a DFB fiber laser is limited to slow laser optical frequency changes, however, due to slow change rates of the thermal mass of the fiber and associated temperature control mechanism.
Although mechanical tuning of a DFB fiber laser by the application of mechanical strain can accomplish rapid changes in the laser optical frequency, such tuning is difficult. The DFB fiber laser manufacturing process weakens the fiber permitting excessive tension to break the fiber. Similarly, wide range mechanical tuning of the fiber can reduce reliability due to the increased chance of fiber breakage. Although some of the problems associated with mechanical tuning can be avoided by limiting the applied mechanical strain to compression loading rather than tension, application of compression to a fiber is difficult to achieve without buckling the fiber. Hence, complex mechanical structures are required to prevent buckling when applying compression-only mechanical tuning.